This invention relates to magnetic head feeding mechanisms in a magnetic recording device, and in particular to a magnetic head feeding mechanism using a rack and a pinion.
Magnetic head feeding mechanisms are known in the art as disclosed in Japanese Utility Second Publication 49-34340 and U.S. Pat. No. 4,428,012. (See FIGS. 1-6 hereof). This prior art feeding device has a guide wherein a carriage is slideably and rotatably mounted on the guide. The magnetic head is mounted on the carriage. A rack is provided on the carriage parallel to the guide. A pinion, mounted on a rotating output shaft of a rotating motor engages the rack. The magnetic head reciprocates along the guide in conjunction with the rotating pinion.
Reference is made to FIG. 1 wherein a perspective view of the prior art device is provided. A guide shaft 51 is affixed on a frame 60 by elastic press plates 59. A carriage 53, supports a magnetic head 52 at a predetermined position, and supports a rack 55. Carriage 53 is guided along guide shaft 51 and is supported upon shaft 51 by metal bushes 68 (FIG. 6). Accordingly, carriage 53 is slideably and rotatably mounted about guide shaft 51. A step motor 56 supported on frame 60, includes an outwardly extending rotating output shaft 61. A pinion 54 is mounted on output shaft 61 and engages rack 55. A spring 58 biases a roller 57 in the direction of arrow A thereby ensuring engagement of rack 55 with pinion 54. Accordingly, as step motor 56 drives rotating output shaft 61, carriage 53 moves along guide shaft 51 without engagement displacement of the rack 55 relative to pinion 54.
Slideable carriage 53 also acts as a stop as it is guided along guide shaft 51. Adjacent slideable carriage 53 is a portion 60a of frame 60 at the one end, and an adjustable screw 62 is mounted on frame 60 adjacent carriage 53 at the other end. As carriage 53 moves in either direction it will eventually contact either adjustable screw 62 or joint 60a, thereby stopping movement in either direction. Accordingly, movement of slideable carriage 53 is limited to this region.
Reference is now made to FIG. 2 wherein the control of the magnetic head feeding device is graphically and schematically shown. In descending order, FIG. 2 depicts the adjustment range of the carriage movement control (adjustable screw 62), the carriage 53 and adjustable screw 62, the direction of rotation of the step motor 56 and track position, and a torque curve of the step motor 56. In the magnetic recording device, the reference track position OOTr, corresponds to the outermost peripheral track position, and the track position is then set so as to count nTr towards the inner periphery At OOTr the phase-position relationship corresponds to an absolute position of carriage 53 and is at a crossing of the torque curve of the step motor 56 with the abscissa.
Therefore, OOTr is a standard value and the positive integer multiples of Tr are inside the periphery, while, the negative integer multiples of Tr are outside the periphery. For example using a four phase step motor 56 feeding at a rate of lTr/l step, when step motor 56 is excited to the excitement phase at the OOTr position, step motor 56 exhibits a continuous torque curve which corresponds to the track position of carriage 53. Stepping motor 56 rotates to any track position of -4Tr, OOTr, 4Tr, . . . , (n.multidot.4) Tr, which correspond to the same excitement phase. The track position to which step motor 56 rotates, depends upon the state of the phase position before excitement. Namely, step motor 56 rotates toward OOTr when the state of the phase position before excitement is between 2Tr and -2Tr.
Carriage 53 moves toward OOTr in the direction of arrow B (FIG. 2) from the inner peripheral side, then stops at the position corresponding to OOTr. Due to inertia forces of the rotor of step motor 56 on carriage 53, carriage 53 overshoots the OOTr position. Carriage 53 is prevented from moving into the outer peripheral side beyond -2Tr by adjustable screw 62. X2 represents surplus space up to adjustable screw 62, Xl represents surplus space between the OOTr position and the actual position of carriage 53 and the diagonally sectioned area between the two is the region in which the position of carriage 53 may be adjusted by adjustable screw 62.
Reference is now made to FIG. 3 and FIG. 4 in which the rack and pinion of the prior art magnetic head feeding mechanism is shown. FIGS. 3 and 4 show three states of pinion 54 relative to rack 55. In order to simplify the explanation, rack 55 is depicted contacting adjustable screw 62.
In normal use pinion 54 rotates in the direction of arrow C, and when rack 55 comes in contact with adjustable screw 62, rack 55 is stopped. However, although rack 55 stops relatively quickly by colliding with adjustable screw 62, pinion 54 does not stop due to its rotational inertia. As a result pinion 54, displaces rack 55 a distance h against spring 58 which is applying pressure in the direction of arrow A. Thus, pinion 54 stops but not before over-rotating through an angle in the direction of arrow C. The above action occurs quite easily during movement of the magnetic recording medium.
While engaged, pinion 54 and rack 55 are often subjected to vibration and shock. Therefore, due to the jumping of carriage 53 during such moments and the resonance of spring 58, momentarily spring 58 cannot apply an engagement force between rack 55 and pinion 54. To minimize the jumping and resonance, the force of spring 58 has been greatly increased in the prior art. However, the stronger the engaging force, the larger the deterioration of step motor 56 due to greater frictional forces, further causing larger electrical consumption in order to improve the property of step motor 56. Therefore, there has been no satisfactory method for preventing the above jumping and resonance, that prevents pinion 54 from overrotating the stop position by angle .theta. in the direction of arrow C.
Overrotation will occur even after adjusting adjustable screw 62, and even though carriage 53 stops by abutting adjustable screw 62. As a result step motor 56 exceeds the proper phase position of the excitement phase by overrotating to -2Tr. On excitation by a signal having the excitement phase associated with the reference track position OOTr (FIG. 2), step motor 56 would rotate in the direction of -4Tr. However, carriage 53 is still adjacent to adjustable screw 62, in a stopped position, therefore carriage 53 cannot move in either of two directions, and suffers from what is known as the "tensile phenomenon."
Moreover, when the overrotation of pinion 54 becomes larger than .theta., the distance h also increases to the state shown in FIG. 4. Thus, although rack 55 stops relatively quickly by contacting adjustable screw 62, as noted above, pinion 54 cannot stop due to rotational inertia of pinion 54 in the direction of arrow C, causing a larger displacement of rack 55 than the distance h discussed above. This larger displacement alters the engagement of pinion 54 and rack 55, and as a result, the fixed regularity in the relationship between rack position and the phase of the exciting signal depicted in FIG. 2 during engagement of rack 55 and pinion 54 disappears. In other words, the fixed regularity exhibited in the phase-position relationship between the absolute position of carriage 53 and the excitement phase of step motor 56 no longer exists, thereby causing the loss of interchangeability of the magnetic recording medium.
Reference is now also made to FIG. 5 in which a sectional view of a magnetic head mounted in accordance with the conventional magnetic head feeding device is provided. A gimbal 64 is mounted on carriage 53, which is composed of plastic material or the like. Magnetic head 52 is mounted on gimbal 64. However, in the conventional magnetic recording device background magnetism often leaks from the motor. Magnetic head 52 has an extremely high magnetic sensitivity so that magnetic head 52 is affected even by a very low level leakage of magnetism from the rest of the magnetic head feeding device. When a motor 66 is provided in close proximity to magnetic head 52 as in the prior art, magnetic head 52 reacts with even smaller amounts of magnetic leakage from motor 66, preventing the natural performance of magnetic head 52. To prevent this interaction, the prior art devices have been provided with a magnetic head shield member 67 mounted on gimbal 64 for shielding the periphery of magnetic head 52 and a magnetic shield member 65 mounted below magnetic head 52 for blocking the leakage of magnetism from motor 66.
Reference is now made to FIG. 6 in which a sectional view of the prior art magnetic head feeding device is provided. Carriage 53, while composed of a plastic, supports metal bushes 68 which allow carriage 53 to be slideably and rotatably mounted on guide shaft 51. An important requirement and feature of a magnetic recording device is its ability to securely access a track position upon receiving an instruction to read/write from or onto the medium. To ensure the positional accuracy of carriage 53 it is essential to maintain the hardness of carriage 53 and to prevent the attrition of the slideable portion, namely metal bushes 68 and guide shaft 51 of the feed mechanism. Carriage 53 may be made of plastic and includes glass or the like, thereby ensuring the hardness thereof. Similarly, metal bush 68 is disposed in the slideable portion of the mechanism thereby preventing the attrition of guide shaft 51 due in part to the surface deposition of the glass or the like on the shaft, as well as the attrition of the carriage 53.
This prior art mechanism, as discussed above, suffers from the disadvantages of overrotation of the pinion, the tensile phenomenon and magnetism sensitivity. Another disadvantage is that due to the need of surplus structure to prevent deterioration and attrition, the pieces of the magnetic recording device are not interchangeable. As a result, mass production of the magnetic recording device according to the conventional rack and pinion magnetic head feeding device has yet to be accomplished.
Accordingly, it is desirable to provide a magnetic head feeding mechanism for a magnetic recording device of simple design to increase position accuracy while enabling mass production of a magnetic recording device having a rack and pinion magnetic head feeding device. By simplifying the magnetic recording device mass production can easily be achieved while providing an improved magnetic memory device having high reliability at a low cost.